mmm 



CONTRIBUTION TO THE PALEONTOLOGY OF TRINIDAD. 43 



further study convinces one that they are mutations of one species. All sizes 

 occur, but a rather large shell measures about 55 mm. in length and 45 in breadth. 



As indicated in the synonymy given above, Karsten's plicatus is referred, 

 tentatively at least, to labiatus. 



Locality. — Ravines on the right and left sides of the trail from Guanoco to 

 Hurupu, on the hillside just above the stream called Rio Colorado. Longitude 

 approximately 3° 59' 6" east of Caracas; latitude approximately 10° 8' north of 

 the equator. 



Geological horizon. — Probably Upper Cretaceous, about equivalent to the 

 Turonian horizon of Europe and the Benton of the United States. Possibly as 

 old as the Gault, but according to Dr. Stanton, not older than that period. 



Genus MODIOLA Lamarck, 1801. 



Modiola cf. alabamensis Aldrich. Plate VII, Figure 9. 



Cf. Modiola alabamensis Aldrich, Bull. Am. Pal., vol. I, p. 68, pi. 5, fig. 13, 1895: Harris, Ibid., 

 vol. II, p. 239, pi. 7, fig. 9, 1897. 



Remarks.— A single fragment of a Modiola shell was found at Soldado. Un- 

 fortunately it is too incomplete for any positive identification or description; but 

 the radiating striae ornamenting the surface almost exactly match those on a 

 specimen of alabamensis from the Lignitic Eocene of Woods Bluff, Alabama, in the 

 Paleontological Museum of Cornell University. It is quite possibly identical 

 with Mr. Aldrich's species. 



Locality.— Bed No. 8, Soldado Rock, Gulf of Paria. 



Geological horizon. — Lignitic Eocene. 



Genus ARCA Linnaeus, 1758. 

 Area (Noetia) sheldoniana new species. Plate VIII, Figures 10, 11. 



Description. — Shell small, rather delicate for the genus, nearly rhomboidal, 

 high and short; posterior slope carinate, very slightly produced; beaks nearly 

 touching, opposite the middle of the row of teeth; moderately inflated; inter- 

 stitial rib present on the posterior half of the valve. 



Length 15; height 13.5; thickness of one valve 6 mm. 



Remarks. — This shell has somewhat the outline of Area (Noetia) ponderosa 

 Say 12 of the Pleistocene and recent faunas of the Atlantic and Gulf coasts. But 

 an examination of the ligamental area shows that it is not ponderosa because the 

 ligament is wholly anterior and ends at the beak, as in the recent west coast 

 species, A. reversa Gray. It is, however, not reversa because it has not so sharp 

 a posterior slope as that species which is, moreover, now limited to the Pacific 

 coast. , 



Thus we have a shell with the outline of the east coast ponderosa and the 

 cardinal area characteristic of the west coast reversa. The fossil shell is inter- 

 mediate between these two species and is an interesting indication of the diver- 



12 Jour. Acad. Nat. Sci. Phila., 1st series, II, p. 267, 1822. 



